The present invention relates to a synchronous switching apparatus for use with a multiple phase power system that controls the opening and closing timing of a power switch to suppress the occurrence of exciting inrush currents and surge voltages, which are hard on system equipment such as transformer, shunt reactor, power-transmission lines and capacitor banks.
In the closing and opening of a power switch, many methods for suppressing transient phenomena that are hard on system equipment have been proposed. For example, xe2x80x9cDevelopment of a gas-blast circuit breaker for 1000 kV GIS,xe2x80x9d included in The 1994 Electric Society National Symposium Proceedings, pages 1453-1455, describes power switching equipment (circuit breaker) in which as means for suppressing surge voltages generated in system equipment such as transformer and shunt reactor, a resistor on the order of 500 to 1000 ohms is inserted before closing the switching equipment. FIG. 7 shows the case in which a shunt reactor is energized by using this resistor insertion technique. In FIG. 7, (1a), (1b), and (1c) are switching devices provided for R, S and T phases, respectively; (2a), (2b), and (2c) are switching devices for closing or opening the switching device for the R, S and T phases, respectively; (8a), (8b) and (8c) are switches for inserting resistors (7a), (7b) and (7c), respectively, which are connected in parallel with the switching devices for the R, S and T phases, respectively; (9a), (9b) and (9c) are reactor banks to be inserted; (5a), (5b) and (5c) are measuring transformers used for measuring the source voltage of each of the R, S and T phases, respectively; and (4) is a control device for issuing closing commands to each switching device (1) and each switch (8).
When the switching devices of the conventional resistor insertion technique configured in this way are used to energize the reactor banks (9), first, the control device (4) issues a closing command to each of the switches (8a), (8b) and (8c), and source voltage are applied to the reactor banks (9) through the resistors (7a), (7b) and (7c). The currents caused by transient surge voltages upon inserting the resistors are rapidly damped by the resistors. Therefore, a voltage of small amplitude and having the same frequency as the source voltage is applied to the reactor banks (9). Subsequently, the control device(4) issues closing commands to each of switching mechanism (2a), (2b) and (2c). Then, when the switching equipment is closed, transient phenomena can be suppressed and exciting inrush currents flowing into the reactor banks (9) can be also suppressed, because a voltage of the same phase as that of the source voltage has already been applied to the reactor banks (9) through the resistors.
However, this method has problems in that the switching equipment is not only comparatively expensive but also large because the method requires that the resistor elements and the switches for inserting the resistors having the capacity needed for each piece of equipment, must be provided inside the switching equipment.
Further, in the case of energizing transmission lines, it is impossible to suppress surges with the inserting resisters if the lines are long. Therefore, when energizing system equipment such as transformer and shunt reactor, in principle, the occurrence of transient exciting inrush currents and surge voltages can be suppressed by energizing at the peak value (an electrical phase angle of 90 degrees) of the source voltage. This is discussed by CIGRE et al. and disclosed in xe2x80x9cControlled Switchingxe2x80x9d, ELECTRA. NO. 164, (1995) and ELECTRA. NO. 165, (1995).
FIG. 8 shows an operating sequence when a transformer is energized using this synchronous switching apparatus. In FIG. 8, (1a), (1b) and (1b) are switching devices provided for the R, S and T phases, respectively; (2a), (2b) and (2c) are switching mechanisms for closing or opening the switching devices for the R, S and T phases, respectively; (3) is a transformer to be energized; (5a), (5b) and (5c) are measuring transformers used for measuring the respective source voltage of the R, S and T phases; (40) is a phase control device for issuing closing commands to the switch mechanism (2) of each switching device (1).
When the transformer (3) is energized using the synchronous switching apparatus configured in this way, first the transformers (5a), (5b) and (5c) used for measuring the respective source voltage of the R. S and T phases detect the zero points of the respective source voltage of the R. S and T phases. The phase control device(40) estimates xe2x80x9ca pole-closing time Tcxe2x80x9d which is the time until an electrical phase angle of a certain ideal angular phase is reached based on the operating time of the switching mechanism as determined from the temperature, operating voltages and past operating history as shown in FIG. 9, and then adjusts xe2x80x9cthe delay time Tdxe2x80x9d for outputting a closing signal such that closing may be established at a closing time Ta corresponding to the target electrical phase angle of each of the R, S and T phases, and provides a closing command to each of the switching mechanism (2a), (2b) and (2c). By closing the switching equipment for the transformer (3) at the predetermined closing time according to this command, in principle, transient phenomena can be suppressed.
Further, xe2x80x9cDevelopment of a gas-blast circuit breaker for 1000 kV GISxe2x80x9d, included in The 1994 Electric Society National Symposium Proceedings, pp. 1453-1455, illustrates a power switch (circuit breaker)xe2x80x9d that suppresses surge voltages generated in system equipment, such as power-transmission lines and capacitor banks, by inserting a resistor on the order of 500 to 1000 ohms before closing the switching equipment, as shown in FIG. 10.
FIG. 10 shows the case of energizing capacitor banks using the switching equipment according to this resistor insertion technique. In this figure, similar reference characters are used to refer to portions that are identical or correspond to those in FIG. 7. In FIG. 10, (9a1), (9b1) and (9c1) show capacitor banks to be energized.
By using the conventional switching devices according to the resistor insertion technique configured as above, when the capacitor banks (9a1), (9b1) and (9c1) are energized, first the control device (4) issues a closing command to each of the switches (8a), (8b) and (8c), and source voltage are applied to the capacitor banks (9a1), (9b1) and (9c1) through the resistors (7a), (7b) and (7c).
A current occurring due to a transient surge voltage upon inserting the resistor(s) is rapidly damped by the resistor(s). Therefore, a voltage having a small amplitude and with the same frequency as the source voltage is applied to the capacitor banks (9a1), (9b1) and (9c1). Subsequently, the control device (4) issues a closing command to each of the switch mechanism (2a),. (2b) and (2c). Then, when the switching equipment is closed, transient phenomena can be suppressed and exciting inrush currents flowing into the capacitor banks (9a1), (9b1) and (9c1) can also be suppressed because a voltage which is in phase with the source voltage has already been applied to the capacitor banks (9a1), (9b1) and (9c1) through the resistors.
However, this method has problems in that the switching equipment is not only comparatively expensive but also has a large size because this method requires that the resistor elements and switches for inserting the resistors having the capacity needed for each piece of equipment, must be provided inside the switching equipment. Further, in the case of energizing transmission lines, it is impossible to suppress surges by inserting resisters for long transmission lines.
Therefore, when energizing system equipment such as transmission lines and capacitor banks, the occurrence of transient exciting inrush currents and surge voltages can be, in principle, suppressed by energizing at the zero point(0) of the electrical phase angle of the source voltage. This is discussed by CIGRE et al. and disclosed in xe2x80x9cControlled Switchingxe2x80x9d, ELECTRA. NO. 164, (1995) and ELECTRA. NO. 165, (1995).
FIG. 11 shows an operating sequence when energizing a transformer using this synchronous switching equipment. In FIG. 11, (1a), (1b) and (1c) are switching devices provided for the R, S and T phases, respectively; (2a), (2b) and (2c) are switching devices for closing or opening the switching devices for the R, S and T phases, respectively; (3a), (3b) and (3c) are transmission lines to be energized, respectively; (5a), (5b) and (5c) transformers are used for measuring the source voltage of the R, S and T phases, respectively; a phase control device (40) issues a closing command to the switch mechanism (2) for each switching device (1).
In the synchronous switching apparatus structured as above, when energizing each of the transmission lines (3a), (3b) and (3c), first, the transformers (5a), (5b) and (5c) used for measuring the source voltage of each of the R, S and T phases detect the zero point of the source voltage of each of the R, S and T phases, respectively. The phase control device (40) estimates xe2x80x9ca pole-closing time Tcxe2x80x9d which is the time until an electrical phase angle of a certain ideal angular phase is reached based on the operating time of the switching mechanism as determined from the temperature, operating voltages and past operating history as shown in FIG. 12, and adjusts xe2x80x9cthe delay time Tdxe2x80x9d for outputting a closing signal such that closing may be established at a closing time Ta corresponding to the target electrical phase angle of each R, S and T phase to provide a closing command to each of the switching mechanisms (2a), (2b), (2c). By closing the switching equipment for the transmission lines (3a), (3b) and (3c) at the predetermined closing time according to this command, in principle, transient phenomena can be suppressed.
However, because the time required for closing switching equipment inevitably varies due to variations in mechanical characteristics and the occurrence of discharge, ideal closing is not always realized.
The present invention has been made to overcome the above-described problems, and an object of the invention is to provide feasible closing timing to the switching equipment for each phase.
The present invention overcomes the above described problems and achieves the above discussed objectives by providing a synchronous switching apparatus for use with a multiple phase power system having a plurality of phases and for detecting a source voltage of each phase and energizing each phase at an electrical phase angle predetermined for each phase. The synchronous switching apparatus includes a plurality of switching devices, one switching device being provided for each phase and opening and closing an impedance load. The synchronous switching apparatus further includes a plurality of switching mechanisms, which close and open the switching devices, and a plurality of voltage measuring transformers, which measure source voltages of the phases. In addition, the synchronous switching apparatus includes a plurality of phase-to-phase voltage measuring transformers, which measure respective phase-to-phase voltages, and a plurality of phase control devices. One phase control device is provided for each phase and issues a command to energize the impedance load with a source voltage at an electrical phase angle in a range predetermined for the phase, in response to detection of a zero point of a source voltage of the phase by the voltage measuring transformer or in response to detection of a zero point of the phase-to-phase voltage by the phase-to-phase voltage measuring transformer.
A second embodiment of the present invention provides a synchronous switching apparatus similar to that of the first embodiment for use with an impedance load in the form of a single-phase core transformer or shunt reactor with a neutral point grounded. For this embodiment, as well as for the third through nineteenth embodiments, the plurality of phases includes a first (R), a second (S), and a third (T) phase, and the plurality of voltage measuring transformers includes a first, a second, and a third voltage measuring transformer, which measure source voltages of the first, second, and third phases, respectively. In addition, the predetermined electrical phase angles of each of the first, second, and third phases are within a range of 90 degrees (voltage peak value of the R, S, and T phases)xc2x190 degrees.
The impedance load is energized with a source voltage via a command sequence, wherein the phase control devices respectively issue a first command for energizing the first (R) phase at the predetermined electrical phase angle of the first phase in response to detection of a zero point of a first (R) phase source voltage by the first voltage measuring transformer, a second command for energizing the third (T) phase at the predetermined electrical phase angle of the third phase in response to detection of a zero point of a third (T) phase source voltage by the third voltage measuring transformer at a time around ⅓ of a cycle after an energizing time of the first (R) phase, and a third command for energizing the second (S) phase at the predetermined electrical phase angle of the second phase in response to detection of a zero point of a second (S) phase source voltage by the second voltage measuring transformer at a time around ⅓ of a cycle after an energizing time of the third (T) phase.
A third embodiment of the present invention provides a synchronous switching apparatus similar to that of the first embodiment for use with an impedance load in the form of a single-phase core transformer or shunt reactor with a neutral point grounded. The plurality of phase-to-phase voltage measuring transformers comprises a first-to-second (R-to-S), a second-to-third (S-to-T), and a third-to-first (T-to-R) phase voltage measuring transformer, which measure a first-to-second, a second-to-third, and a third-to-first phase voltage, respectively. The predetermined electrical phase angles of each of the first-to-second phase voltage, the second-to-third phase voltage, and the third-to-first phase voltage are within a range of 60 degrees xc2x120degrees.
The impedance load is energized with a source voltage via a command sequence, wherein the phase control devices respectively issue a first command for energizing the first (R) phase at the predetermined electrical phase angle of the first-to-second (R-to-S) phase voltage in response to detection of a zero point of the first-to-second phase voltage by the first-to-second phase voltage measuring transformer, a second command for energizing the third (T) phase at the predetermined electrical phase angle of the third-to-first (T-to-R) phase voltage in response to detection of a zero point of the third-to-first (T-to-R) phase voltage by the third-to-first phase voltage measuring transformer at a time around ⅓ of a cycle after an energizing time of the first phase, and a third command for energizing the second (S) phase at the predetermined electrical phase angle of the second-to-third (S-to-T) phase voltage in response to detection of a zero point of the second-to-third (S-to-T) phase voltage by the second-to-third phase voltage measuring transformer at a time around ⅓ of a cycle after an energizing time of the third (T) phase.
A fourth embodiment of the present invention provides a synchronous switching apparatus similar to that of the first embodiment for use with an impedance load in the form of a three-phase core transformer or shunt reactor having star-connected windings with a neutral point grounded. The plurality of voltage measuring transformers includes a first and a third voltage measuring transformer, which measure source voltages of the first and third phases, respectively. The predetermined electrical phase angle of the first phase is within a range of 90 degrees (voltage peak value of the R phase) xc2x120 degrees, and the electrical phase angle of the third phase is within a range of 60 degrees xc2x120 degrees.
The impedance load is energized with a source voltage via a command sequence, wherein the phase control devices respectively issue a first command for energizing the first (R) phase at the predetermined electrical phase angle of the first phase in response to detection of a zero point of a first (R) phase source voltage by the first voltage measuring transformer, a second command for energizing the third (T) phase at the predetermined electrical phase angle of the third phase in response to detection of a zero point of a third (T) phase source voltage by the third voltage measuring transformer at a time around xc2xc of a cycle after an energizing time of the first (R) phase, and a third command for energizing the second (S) phase at any time after the energizing of the third (T) phase.
A fifth embodiment of the present invention provides a synchronous switching apparatus similar to that of the first embodiment for use with an impedance load in the form of a single-phase core transformer or shunt reactor with a neutral point grounded. The plurality of voltage measuring transformers includes a first and a second voltage measuring transformer, which measure source voltages of the first and second phases, respectively.
The predetermined electrical phase angle of the first phase is within a range of 90 degrees (voltage peak value of the R phase) xc2x120 degrees, and the predetermined electrical phase angle of the second phase is within a range of xe2x88x9230 degrees xc2x120 degrees.
The impedance load is energized with a source voltage via a command sequence, wherein the phase control devices respectively issue a first command for energizing the first (R) phase at the predetermined electrical phase angle of the first phase in response to detection of a zero point of the first (R) phase source voltage by the first voltage measuring transformer, a second command for energizing a second (S) phase at the predetermined electrical phase angle of the second phase in response to detection of a zero point of a second (S) phase source voltage by the second voltage measuring transformer at a time around xc2xc of a cycle after an energizing time of the first (R) phase, and a third command for energizing the third (T) phase at any time after the energizing of the second phase.
A sixth embodiment of the present invention provides a synchronous switching apparatus similar to that of the first embodiment for use with an impedance load in the form of a single-phase core transformer or shunt reactor with a neutral point grounded. The plurality of phase-to-phase voltage measuring transformers includes a first-to-second (R-to-S) and a third-to-first (T-to-R) phase voltage measuring transformer, which measure a first-to-second and a third-to-first phase voltage, respectively.
The predetermined electrical phase angle of the first-to-second phase voltage is within a range of 60 degrees xc2x120 degrees, and the predetermined electrical phase angle of the third-to-first phase voltage is within a range of 30 degrees xc2x120 degrees.
The impedance load is energized with a source voltage via a command sequence, wherein the phase control devices respectively issue a first command for energizing the first (R) phase at the predetermined electrical phase angle of the first-to-second (R-to-S) phase voltage in response to detection of a zero point of the first-to-second phase voltage by the first-to-second phase voltage measuring transformer, a third command for energizing the third (T) phase at the predetermined electrical phase angle of the third-to-first (T-to-R) phase voltage in response to detection of a zero point of a third-to-first (T-to-R) phase voltage by the third-to-first phase voltage measuring transformer at a time around ⅓ of a cycle after an energizing time of the first (R) phase, and a second command for energizing the second (S) phase at any time after the energizing of the third (T) phase.
A seventh embodiment of the present invention provides a synchronous switching apparatus similar to that of the first embodiment for use with an impedance load in the form of a three-phase core transformer or shunt reactor having star-connected windings with a neutral point grounded. The plurality of phase-to-phase voltage measuring transformers comprises a first-to-second (R-to-S), and a second-to-third (S-to-T), which measure a first-to-second and a second-to-third phase voltage, respectively.
The predetermined electrical phase angles of the first-to-second and the second-to-third phase voltage are within a range of 60 degrees xc2x120 degrees and xe2x88x9260 degrees xc2x120 degrees, respectively.
The impedance load is energized with a source voltage via a command sequence, wherein the phase control devices respectively issue a first command for energizing the first (R) phase at the predetermined electrical phase angle of the first-to-second (R-to-S) phase voltage in response to detection of a zero point of the first-to-second (R-to-S) phase voltage by the first-to-second phase voltage measuring transformer, a second command for energizing the second (T) phase at the predetermined electrical phase angle of the second-to-third (S-to-T) phase voltage in response to detection of a zero point of the second-to-third (S-to-T) phase voltage by the second-to-third phase voltage measuring transformer at a time around ⅓ of a cycle after an energizing time of the first phase (R phase), and a third command for energizing the third (T) phase at any time after the energizing of the second (S) phase.
An eighth embodiment of the present invention provides a synchronous switching apparatus similar to that of the first embodiment for use with an impedance load in the form of a three-phase core transformer or shunt reactor having star-connected windings with a neutral point ungrounded, or a delta connection transformer or shunt reactor. The plurality of voltage measuring transformers includes a first and a third voltage measuring transformer, which measure source voltages of the first and third phases, respectively. The predetermined electrical phase angles of the first and third phases are within a range of 120 degrees xc2x120 degrees and 90 degrees xc2x120 degrees, respectively.
The impedance load is energized with a source voltage via a command sequence, wherein the phase control devices respectively issue a first command for energizing the second (S) phase at any time, a second command for energizing the first (R) phase at the predetermined electrical phase angle of the first (R) phase in response to detection of a zero point of a first (R) source voltage by the first voltage measuring transformer after the energizing of the second (S) phase, and a third command for energizing the third (T) phase at the predetermined electrical phase angle of the third (T) phase in response to detection of a zero point of a third (T) phase source voltage by the third voltage measuring transformer at a time around ⅓ of a cycle after an energizing time of the first (R) phase.
A ninth embodiment of the present invention provides a synchronous switching apparatus similar to that of the first embodiment for use with an impedance load in the form of a three-phase core transformer or shunt reactor having star-connected windings with a neutral point ungrounded, or a single-phase core and three-phase core delta connection transformer or shunt reactor. The plurality of voltage measuring transformers includes a second and a third voltage measuring transformer, measuring source voltages of the second and third phases, respectively. The predetermined electrical phase angles of the second and third phases are within a range of xe2x88x92120 degrees xc2x120 degrees and 90 degrees xc2x120 degrees, respectively.
The impedance load is energized with a source voltage via a command sequence, wherein the phase control devices respectively issue a first command for energizing the first (R) phase at any time, a second command for energizing the second (S) phase at the predetermined electrical phase angle of the second (S) phase in response to detection of a zero point of a second (S) phase source voltage by the second voltage measuring transformer after the energizing of the first (R) phase, and a third command for energizing the third (T) phase at the predetermined electrical phase angle of the third (T) phase in response to detection of a zero point of a third (T) phase source voltage at a time around ⅓ of a cycle after an energizing time of the second (S) phase.
A tenth embodiment of the present invention provides a synchronous switching apparatus similar to that of the first embodiment for use with an impedance load in the form of a three-phase core transformer or shunt reactor having star-connected windings with a neutral point ungrounded, or a single-phase core and three-phase core delta connection transformer or shunt reactor. The plurality of phase-to-phase voltage measuring transformers includes a first-to-second (R-to-S phase) and a third-to-first (T-to-R) phase voltage measuring transformer, which measure a first-to-second and a third-to-first phase voltage, respectively. The predetermined electrical phase angles of the first-to-second and third-to-first phase voltages are within a range of 90 degrees xc2x120 degrees and 60 degrees xc2x120 degrees, respectively.
The impedance load is energized with a source voltage via a command sequence, wherein the phase control devices respectively issue a first command for energizing the second (S) phase at any time, a second command for energizing the first (R) phase at the predetermined electrical phase angle of a first-to-second (R-to-S) phase voltage in response to detection of a zero point of a first-to-second (R-to-S) phase voltage by the first-to-second phase voltage measuring transformer after an energizing time of the second (S) phase, and a third command for energizing the third (T) phase at the predetermined electrical phase angle of a third-to-first (T-to-R) phase voltage in response to detection of a zero point of a third-to-first (T-to-R) phase voltage by the third-to-first phase voltage measuring transformer at a time around ⅓ of a cycle after an energizing time of the first (R) phase.
An eleventh embodiment of the present invention provides a synchronous switching apparatus similar to that of the first embodiment for use with an impedance load in the form of a three-phase core transformer or shunt reactor having star-connected windings with a neutral point ungrounded, or a single-phase core and three-phase core delta connection transformer or shunt reactor. The plurality of phase-to-phase voltage measuring transformers includes a second-to-third (S-to-T) and a third-to-first (T-to-R) phase voltage measuring transformer, which measure a second-to-third and a third-to-first phase voltage, respectively. The predetermined electrical phase angles of the second-to-third and the third-to-first phase voltages are within a range of xe2x88x92150 degrees xc2x120 degrees and 60 degrees xc2x120 degrees, respectively.
The impedance load is energized with a source voltage via a command sequence, wherein the phase control devices respectively issue a first command for energizing the first (R) phase at any time, a second command for energizing the second (S) phase at the predetermined electrical phase angle of a second-to-third (S-to-T) phase voltage in response to detection of a zero point of a second-to-third (S-to-T) phase voltage by the second-to-third phase voltage measuring transformer after an energizing of the first (R) phase, and a third command for energizing the third (T) phase at the predetermined electrical phase angle of a third-to-first (T-to-R) phase voltage in response to detection of a zero point of a third-to-first (T-to-R) phase voltage by the third-to-first phase voltage measuring transformer at a time around ⅓ of a cycle after an energizing time of the second (S) phase.
A twelfth embodiment of the present invention provides a synchronous switching apparatus similar to that of the second embodiment, but which is for use with an impedance load in the form of capacitor banks with a neutral point grounded or transmission lines without an electric charge. In addition, the predetermined electrical phase angles of each of the first, second, and third phases are within a range of 0 degrees (zero voltage points of the R, S, and T phases) xc2x120 degrees.
A thirteenth embodiment of the present invention provides a synchronous switching apparatus similar to that of the third embodiment, but which is for use with an impedance load in the form of capacitor banks with a neutral point grounded or transmission lines without an electrical charge. In addition, the predetermined electrical phase angles of each of the first-to-second phase voltage, the second-to-third phase voltage, and the third-to-first phase voltage are within a range of xe2x88x9230 degrees xc2x120 degrees.
A fourteenth embodiment of the present invention provides a synchronous switching apparatus similar to that of the first embodiment for use with an impedance load in the form of capacitor banks with a neutral point ungrounded. The plurality of voltage measuring transformers includes a second and a third voltage measuring transformer, which measure source voltages of the second and third phases, respectively. The predetermined electrical phase angles of the second and third phases are within a range of 0 degrees xc2x120 degrees and 30 degrees xc2x120 degrees, respectively.
The impedance load is energized with a source voltage via a command sequence, wherein the phase control devices respectively issue a first command for energizing the first (R) phase at any time, a second command for energizing the third (T) phase at the predetermined electrical phase angle of the third (T) phase in response to detection of a zero point of the third (T) phase source voltage by the third voltage measuring transformer after an energizing of the first (R) phase, and a third command for energizing the second (S) phase at the predetermined electrical phase angle of the second (S) phase in response to detection of a zero point of a second (S) phase source voltage by the second voltage measuring transformer at a time around xc2xc of a cycle after an energizing time of the third (T) phase.
A fifteenth embodiment of the present invention provides a synchronous switching apparatus similar to that of the eighth embodiment, but which is for use with an impedance load in the form of capacitor banks with a neutral point ungrounded. In addition, the predetermined electrical phase angle of the first phase is within a range of 30 degrees xc2x120 degrees, and the predetermined electrical phase angle of the third phase is within a range of 0 degrees xc2x120 degrees. Also, the respective phase control device issues the third command for energizing the third (T) phase at the predetermined electrical phase angle of the third (T) phase in response to detection of a zero point of a third (T) phase source voltage by the third voltage measuring transformer at a time around xc2xc of a cycle after a energizing time of the first (R) phase.
A sixteenth embodiment of the present invention provides a synchronous switching apparatus similar to that of the first embodiment for use with an impedance load in the form of capacitor banks with a neutral point ungrounded. The plurality of voltage measuring transformers includes a first and a third voltage measuring transformer, which measure source voltages of the first and third phases, respectively. The predetermined electrical phase angles of the first and third phases are within a range of 30 degrees xc2x120 degrees and 0 degrees xc2x120 degrees, respectively.
The impedance load is energized with a source voltage via a command sequence, wherein the phase control devices respectively issue a first command for energizing the second (S) phase at any time, a second command for energizing the first (R) phase at the predetermined electrical phase angle of the first (R) phase in response to detection of a zero point of a first (R) phase source voltage by the first voltage measuring transformer after the energizing of the second (S) phase, and a third command for energizing the third (T) phase at the predetermined electrical phase angle of the third (T) phase in response to detection of a zero point of a third (T) phase source voltage by the third voltage measuring transformer at a time around xc2xc of a cycle after a energizing time of the first (R) phase.
A seventeenth embodiment of the present invention provides a synchronous switching apparatus similar to that of the first embodiment for use with an impedance load in the form of capacitor banks with a neutral point ungrounded. The plurality of phase-to-phase voltage measuring transformers includes a second-to-third (S-to-T) and a third-to-first (T-to-R) phase voltage measuring transformer, which measure a second-to-third and a third-to-first phase voltage, respectively. The predetermined electrical phase angles of the second-to-third and the third-to-first phase voltages are within a range of xe2x88x9230 degrees xc2x120 degrees and 0 degrees xc2x120 degrees, respectively.
The impedance load is energized with a source voltage via a command sequence, wherein the phase control devices respectively issue a first command for energizing the first (R) phase at any time, a second command for energizing the third (T) phase at the predetermined electrical phase angle of a third-to-first (T-to-R) phase voltage in response to detection of a zero point of a third-to-first (T-to-R) phase voltage by the third-to-first phase voltage measuring transformer after the energizing of a first (R) phase, and a third command for energizing the second (S) phase at the predetermined electrical phase angle of a second-to-third (S-to-T) phase voltage in response to detection of a zero point of a second-to-third (S-to-T) phase voltage by the second-to-third phase voltage measuring transformer at a time around xc2xc of a cycle after an energizing time of the third (T) phase.
An eighteenth embodiment of the present invention provides a synchronous switching apparatus similar to that of the tenth embodiment, but which is for use with an impedance load in the form of capacitor banks with a neutral point ungrounded. In addition, the predetermined electrical phase angle of the first-to-second phase voltage is within a range of 0 degrees xc2x120 degrees, and the predetermined electrical phase angle of the third-to-first phase voltage is within a range of xe2x88x9230 degrees xc2x120 degrees. Also, the respective phase control device issues the third command for energizing the third (T) phase at the predetermined electrical phase angle of the third-to-first (T-to-R) phase voltage in response to detection of a zero point of a third-to-first (T-to-R) phase voltage by the third-to-first phase voltage measuring transformer at a time around xc2xc of a cycle after a energizing time of the first (R) phase.
A nineteenth embodiment of the present invention provides a synchronous switching apparatus similar to that of the first embodiment for use with an impedance load in the form of capacitor banks with a neutral point ungrounded. The plurality of phase-to-phase voltage measuring transformers comprises a first-to-second (R-to-S) and a second-to-third (S-to-T) phase voltage measuring transformer, which measure a first-to-second and a second-to-third phase voltage, respectively. The predetermined electrical phase angles of the first-to-second and the second-to-third phase voltages are within a range of xe2x88x9230 degrees xc2x120 degrees and 0 degrees xc2x120 degrees, respectively.
The impedance load is energized with a source voltage via a command sequence, wherein the phase control devices respectively issue a first command for energizing the third (T) phase, a second command for energizing the second (S) phase at the predetermined electrical phase angle of a second-to-third (S-to-T) phase voltage in response to detection of a zero point of a second-to-third (S-to-T) phase voltage by the second-to-third phase voltage measuring transformer after the energizing of the third (T) phase, and a third command for energizing the first (R) phase at the predetermined electrical phase angle of a first-to-second (R-to-S) phase voltage in response to detection of a zero point of a first-to-second (R-to-S) phase voltage by the first-to-second phase voltage measuring transformer at a time around xc2xc of a cycle after an energizing time of the second (S) phase.
A twentieth embodiment of the present invention provides a synchronous switching apparatus similar to that of the first embodiment, but further includes surge absorbers, which are provided between respective phases and ground, for respectively suppressing surge voltages of respective phases. In addition, surge absorbers are provided between respective phases for suppressing phase-to-phase surge voltages.